1. Field of the Invention
The present invention relates to a backlight assembly and a liquid crystal display (LCD) device having the backlight assembly and, more particularly, to a thinner backlight assembly having improved color reproducibility and image display quality.
2. Description of the Related Art
Image display devices, especially liquid crystal displays (LCDs), are desirable in many electronic devices such as mobile communication terminals, digital cameras, laptop computers, monitors, etc., because they can be thinner and have lower driving voltage and power consumption than either cathode ray tubes (CRTs) or plasma display panels (PDPs). The liquid crystals used in LCDs exhibit anisotropic refraction and anisotropic dielectric constant. Since the LCD neither generates nor emits light, it requires a backlight assembly to supply incident light. A conventional backlight assembly includes either a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED) as a light source. The CCFL has low manufacturing costs, high luminance but is large in size and required a high driving voltage. Small-screen LCDs such as used in a mobile communication terminal require the use of LEDs, but these provide a point light source. A light-guide plate and a diffusion sheet are required in order to uniformly distribute light from a point light source onto a surface.
Materials that can be used for the light-guiding plate include polymethylmethacrylate (PMMA) and polycarbonate (PC). PMMA has good optical characteristics, high hardness and good plasticity, while PC has high heat resistance. In order to make thinner small-screen LCD device, the thickness of the light-guiding plate, which is the thickest element of the backlight assembly, has to be decreased. However, decreasing the thickness of the light-guiding plate decreases its heat resistance. In order to improve the heat resistance of the light-guiding plate, the light-guiding plate includes PC, which has high heat resistance.
The diffusion sheet that is employed with a light-guiding plate includes both a bead layer on its surface facing the light-guiding plate and a bead layer on its other surface to diffuse the light. These “lower” and “upper” bead layers are made of PMMA. The PMMA of the beads in the lower bead layer are harder than the PC used in the light-guiding plate. Abrasion between the beads of the diffusion sheet and the light guide plate can cause scratches that degrade the image display quality of the LCD device.
To generate white light, the backlight assembly employs a blue light LED having a yellow fluorescent material disposed on it. The blue light and a yellow light are combined to form a white light. However, in this arrangement the blue light predominates, thereby degrading the LCD's color reproducibility.